It is known to practice ellipsometry, polarimetry, reflectometry and spectophotometry to investigate samples with electromagnetic beams. Typically, samples investigated have a substantially smooth surface and the procedure involves taking data and regressing a mathematical model thereonto. Where a sample surface is not substantially smooth, however, but rather is rough or textured, it has been found that the typical approach leads to determination of values for physical and optical properties results which are not correct. While the data might appear qualitatively correct, it has been found that there is generally an offset between, for instance, values for the refractive index and extinction coefficient for a thin film on said rough or textured surface, as compared to values for the same thin film on a sample with a substantially smooth surface. This is because during measurements of rough or textured surfaces with spectroscopic electromagnetic radiation, much of the measurement beam can be scattered away from the detector. This significantly reduces the overall intensity reaching the ellipsometer detector. While it is true that Spectroscopic Ellipsometry (SE) measurements collect a ratio of light components and do not require the absolute intensity, the detected light can also be affected by the scattering or roughness. The effect of roughness on the data can be measured from an uncoated rough surface and then applied to coated rough surfaces to correct for the roughness effects on SE data. This is demonstrated to improve the accuracy of coating measurements on rough and textured surfaces.
As disclosed in Parent application Ser. No. 12/315,898, it is well known in the art to cause an electromagnetic beam to reflect from a sample, and by monitoring change in, for example, the intensity and/or polarization state of said beam resulting from interaction with the sample, determine properties of the sample, (eg. thickness of thin films on the sample surface, and optical constants). It is also known that where a sample surface reflects specularly essentially all incident electromagnetic radiation can be reflected from the sample into a detector and good data will typically be developed thereby. A problem can occur, however, where a sample has an irregular surface, as incident electromagnetic radiation becomes scattered by what amounts to the effects of said beam effectively approaching the sample surface at different angles and planes of incidence, at different locations thereon. When this occurs a large majority of the electromagnetic radiation which reflects from the sample surface is often directed other than into a detector, or is scattered, rather than specularly reflected thereinto, which scattered electromagnetic radiation causes problems in analysis of acquired data. The intensity of a collected portion of a reflected beam can then become too weak to be used in sample analysis and attempts to increase the intensity entering a detector, without consideration of from where on an irregular sample surface the additional collected electromagnetic radiation reflects, can lead to data which is noisy, depolarized, based on uncertain angles-of-incidence, and therefore can not be reliably analyzed to provide good results.
It is further known to place samples on stages in ellipsometer and the like systems, and to cause a polarized beam of electromagnetic radiation to impinge on said sample at an oblique angle thereto, interact with said sample and then enter a detector. It is also known that the “tilt” of a sample surface at a specific location thereon can affect realized angle and plane-of-incidence values actually achieved. Further, it is known to adjust the vertical height of the stage to position a sample such that a beam of electromagnetic radiation reflecting therefrom enters a detector. And, it is known to use a beam of electromagnetic radiation comprising a range of wavelengths, (eg. which can be smaller or larger than a facet feature on a sample to enable), investigation thereof).
Continuing, as it is relevant, Patent to Abraham et al., U.S. Pat. No. 6,091,499 is disclosed as it describes a method and system for automatic relative adjustment of samples in relation to an ellipsometer. Paraphrasing, said Abraham et al. system basically comprises:                a system for orienting a sample on a stage in an ellipsometer system comprising a first light source, a polarizer, said stage, an analyzer and a detector;        said system further comprising a detection system having a second light source, wherein said detection system is independently adjustable in relation to said ellipsometer, and wherein said detection system can be electronically locked into position relative to said ellipsometer so that said ellipsometer and said detection system can be adjusted as one unit in relationship to said stage, wherein said detection system can detect both a tilt of a sample placed onto said stage, and a distance of said sample from a coordinate source of the ellipsometer in two perpendicular axes; and        said system further comprising an adjusting device, wherein said adjusting device can adjust tilt of said stage, and wherein said adjusting device can adjust the position of said ellipsometer and detection system when in an electronically locked relationship with respect to one another.The 499 Patent drawings show a single source, (identified as (21)), provides, via beam splitters and reflection means, normal and oblique angle-of-incidence electromagnetic beams to a sample, which normal and oblique angle-of-incidence electromagnetic beams are each intercepted by a different detector, (identified as (24) and (25) respectively), after reflecting from the sample. The associated ellipsometer system comprises a separate source, (identified as (11)).        
Additional known related Patents are:    Patent to Coates U.S. Pat. No. 4,373,817;    Patent to Coates U.S. Pat. No. 5,045,704;    RE. 34,783 to Coates;    Patent to Mikkelsen et al., U.S. Pat. No. 6,600,560;    Patent to Fanton et al., U.S. Pat. No. 5,596,411;    Patent to Piwonka-Corle et al., U.S. Pat. No. 5,910,842;    Patent to Piwonka-Corle et al., U.S. Pat. No. 5,608,526;    Patent to Bareket, U.S. Pat. No. 5,889,593;    Patent to Norton et al., U.S. Pat. No. 5,486,701;    Patent to Aspnes et al., U.S. Pat. No. 5,900,939;    Patent to Aspnes et al., U.S. Pat. No. 5,798,837;    Patent to Rosenscwaig et al., U.S. Pat. No. 5,412,473;    Patent to Carter et al., U.S. Pat. No. 5,771,094;    Patent to Liphardt, U.S. Pat. No. 7,136,162;    PCT Application Publication WO 99/45340;    Published Application of Stehle et al., No. US2002/0024668 A1.
Additionally, a recent computer search using the words “solar cell” and “sample tilt” provided no hits, while using the words “solar cell” and “substrate tilt” provided one hit each for Patents and Published Applications, (eg. U.S. Pat. No. 5,388,635 and Published Application US 2007/0267711), and using the words “solar cell” and “stage tilt” provided two hits each for Published Applications, (eg. US 2006/0048800 and 2004/0056779). None of these identified references are considered relevant.
Provisional Application Ser. No. 61/126,233 filed May 2, 2008 in incorporated herein by reference.
As the system of the present invention includes intensity controlling “crossed-polarizers”, U.S. Patents and Published Applications were identified which include the terms “crossed-polarizer” and “ellipsometry” or “ellipsometer”, and are:
Patents
    U.S. Pat. Nos. 7,236,221; 7,221,420; 7,211,304; 7,163,724; 7,083,835; 7,061,561; 6,934,024; 6,798,511; 6,693,711; 6,112,114; 5,787,890; 5,303,709; 4,097,110; 7,170,574;Published Applications    2006/0215158; 2006/0203164; 2006/0193975; 2005/0286001; 2005/0270459; 2005/0270458; 2005/0024561; 2004/0189992; 2004/0179158; 2003/0227623; 2003/0227623; 2002/0091323; 2006/0141466; 2006/0115640; 2006/0099135; 2005/0270458; 2005/0128391; 2004/0208350; 2004/0189992; 2003/0227623; 2002/0091323.
A USPTO data base computer search of both Patents and Published Applications using “scatter matrix” and “ellipsometer” or “ellipsometry” did not produce any hits. Where “correction matrix” is substituted a Patent to Jellison Jr. et al. No. 5,956,147 was identified, but no Published Applications were found. The 147 Patent concerns calibration of a two modulator generalized ellipsometer, however, and not to investigation of rough or textured samples.
Finally, while there is no known published disclosure thereof, Applicants have heard, “through the grapevine”, that another entity (ie. Sentech), is using a large sample tilt technique similar to that disclosed herein, to facilitate investigation of solar cells. However, Applicants believe this alternative use is of very recent implementation and, for instance, does not involve use of spectroscopic electromagnetic radiation nor involve application of a sample stage rotation. Said usage is not known to involve the correction mechanism which is the focus of the present invention.
An approach to investigating a sample with a “regularly” textured surface, (ie. it comprises a surface having a repeated faceted pattern thereupon) and/or a surface characterized by an irregular array of faceted structures, would provide utility. If possible, such an approach would allow a researcher to collect an increased amount of “information containing” electromagnetic radiation which reflects from said sample textured surface and enters a detector to produce good data. This is especially the case where a correction approach allows arriving at values for thin film characteristics determined on rough or textured surfaces which match those determined from samples with smooth surfaces. It is such an approach that is subject of the present invention.
The present invention provides an approach to coordinating results obtained from investigation of a thin film present on a sample with a rough or textured sample to results obtained from investigating of a thin film present on a sample with a substantially smooth surface.